Every day, we experience sound in our environment, such as the sounds from television and radio, household appliances, and traffic. Normally, we hear these sounds at safe levels that do not affect our hearing. However, when we are exposed to harmful noise—sounds that are too loud or loud sounds that last a long time—sensitive structures in our inner ear can be damaged, causing noise-induced hearing loss (NIHL). These sensitive structures, called hair cells, are small sensory cells in the inner ear that convert sound energy into electrical signals that travel to the brain. Once damaged, our hair cells cannot grow back.

Scientists once believed that the pure force of vibrations from loud sounds caused the damage to hair cells. Instead, recent studies have shown that exposure to harmful noise triggers the formation of molecules inside the ear that can damage or kill hair cells.